Innovative approaches are helping to improve road resilience and life safety across one of the most flood-prone regions in New South Wales, a conference has heard.

Speaking at the Climate Smart Engineering Conference hosted by Engineers Australia, Jared Crossley and Anna Luong, Principal Civil Engineer and Civil Engineer at multi-national infrastructure advisory firm AECOM, described how innovative approaches are being employed as part of the Hawkesbury-Nepean Valley Flood Evacuation Road Resilience program.

The presentation comes amid growing concern about flood risk across the Hawkesbury-Nepean Valley.

Covering an area of more than 500 square kilometres of floodplain west of Sydney, the Valley is considered to be one of the most significant regions of unmitigated flood risk in Australia.

All up, it has seen more than 100 major or moderate floods since records began in the late 1700s.

In March 2021, major flooding saw evacuation orders issued for thousands of households and necessitated hundreds of rescues. One man died after being trapped by floodwater in his car.

Further evacuation orders were issued across the Valley in March 2022 after parts of NSW received their highest March monthly rainfall on record.

Four months later in July 2022, significant evacuation orders were issued as floodwaters rose across the Valley. The town of Wallacia was completely cut off after the Park Road evacuation route at Jerrys Creek was cut by floodwater.

From a landscape point of view, the region’s high-risk profile is driven by its composition of three interconnected floodplains. This composition sees flood events occur almost simultaneously and overlap across each of the three plains.

The impact is further compounded by a ‘bathtub effect’. This arises as narrow sandstone gorges create natural ‘choke points’ between Sackville and Brooklyn as floodwater and rainwater flows downstream via the Hawkesbury Nepean River.

During heavy rain, these choke points see floodwaters back up and rise rapidly. This can result in widespread flooding across the Valley.

Compounding these concerns is the area’s rapid population growth.

This is taking place amid increasing development and population pressures across Sydney’s outer west.

As things stand, the Valley is currently home to more than 140,000 residents and workers.

On current projections, this population is expected to double between now and 2050.

That raises serious questions about loss of life as large numbers of people need to evacuate quickly during a flood.

When floods occur, evacuees rely upon a network of fourteen road evacuation routes.

As noted in recent flood risk modelling, however, these currently provide insufficient road capacity to evacuate on time.

The importance of efficient road movement is further underlined by the fact that some evacuation routes can be cut by floodwater.

Depending on the specific behaviour of individual floods, this can happen early on even in relatively small floods.

As a result, the road network needs to enable fast evacuation.

Led by Transport and Infrastructure NSW, the aforementioned road resilience program aims to improve the climate resilience of the Valley by improving immunity of road evacuation routes to flooding and increasing the efficiency of the routes.

It aims to reduce evacuation times and thus lower the risk-to-life which is presented by floods.

To achieve this, actions are set to include:

• Road shoulder widening to improve traffic flow during evacuations and to ensure that more people can safely escape before roads are cut. This involves widening of existing road shoulders in the outbound direction along several evacuation routes. It will provide two outbound evacuation lanes whilst maintaining a single inbound lane for emergency improvements.
• Pinch point improvements to intersections along evacuation routes. These will improve turning paths where two outbound evacuation lanes are not able to be accommodated.
• A series of drainage improvements to improve flow capacity and reduce overland flow across evacuation routes. These include upsizing and optimising existing channels and culverts as well as raising road and bridge levels.

Scheduled to be delivered over an eleven-year period beginning in 2019, the program is currently in the Concept Design stage.

A final business case and environmental approvals are expected this year before construction occurs over a five-year period from 2026.

During the presentation, Crossley and Luong shared a number of innovative approaches which are being employed to deliver better outcomes.

These were shared in order to demonstrate how innovation can be applied in an environment where some stakeholders are resistant to change.

First, there has been enhanced collaboration during design.

This is not so much of a high-tech innovation but more of a better way of working.

As well as involving the traditional multi-disciplinary engineering team, the design team undertook early engagement with their colleagues from AECOM’s environment, resilience and sustainability disciplines.

This involved a series of early workshops during which alternative resilient design approaches were considered.

Such an approach challenged the design team to adopt a more holistic outlook when deciding upon the design strategy. It also improved confidence across the entire team that the design would deliver resilient and sustainable outcomes.

Next, there were improvements in design processes. These were made using tools which are readily available but which nonetheless delivered significant value.

When collecting data from site, the team used photographs that were obtained from 360-degree hand-held cameras. These were uploaded into construction site viewing software program HoloBuilder. Within HoloBuilder, the captured imagery was readily mapped and viewable in 3D in a manner which is similar to Google Street View.

Compared with traditional 2D photos, the 3D imagery provided greater context when planning design strategy. The imagery also facilitated clearer and more intuitive communication during stakeholder engagement – especially when dealing with those who had not physically been out to site.

The team also developed an online ArcMap GIS platform. This brought together project locations, environmental concerns, survey and utilities information along with the proposed design. It provided the team with further context in design decision making.

Third, the team used artificial intelligence for the design of 42 kilometres of shoulder widening.

A particular focus in this area involves the condition assessment of the existing pavement.

Under a conventional approach, the pavement team would need to spend many hours on site to complete a detailed visual inspection of existing pavement condition.

This would have necessitated traffic control and lane closures for several weeks.

Further disruptions would then have followed during the subsequent geotechnical investigation.

Instead, the team completed a simple drive-through of the routes from which video footage was captured by a standard Go Pro camera. This was uploaded to a platform known as INSPECH. Enabled by AI, the program was able to identify defects in the pavement surface and classify the surface condition along the route (of course, the output needed to be validated).

Using the information, the design team was able to make better decisions about where geotechnical investigation work was needed as well as where design efforts should be focused.

The result was greater efficiency in terms of time on site, lower levels of community disruption and a reduction in waste that is generated where boreholes need to be drilled on account of poor reconnaissance.

Fourth, there was resilient and sustainable design.

Whilst the project’s primary focus revolved around resilience and safety, the team also recognised the need to minimise impacts upon environmentally sensitive sites.

Toward this end, measures that have been considered include alternative batter slope profiles such as steeper batters for roadside drains (to allow greater drainage capacity without necessitating tree or plant removal), shifting the road carriageway and adopting hidden pipe networks.

This contrasted with a ‘business as usual’ approach, whereby environmental impacts may be noted but may not be the focus of meaningful action.

Finally, there is the embedding of resilience and sustainability into pavements.

One such initiative involves foamed bitumen stabilisation combined with a sealed shoulder.

Foamed bitumen stabilisation involves taking existing asphalt, pulverising it and adding a binding agent. The pavement is then laid and compacted back onto the road.

Use of this method enables the rehabilitation of the existing running lane along with the provision of a stabilised base for both the running lane and the shoulder in a manner which uses less material and ultimately requires less maintenance. It also seals the shoulder to deliver a pavement which is more durable.

When considering innovative approaches, Luong encourages engineers to maintain focus on the broader picture of their work.

“It can be easy for us as engineers to get caught up in the technical detail of things,” Luong said.

“We sit there managing calculations, reports and drawings and decide upon what design parameters take priority.

“We can spend all day thinking about how to store images, collect data and assess pavements.

“(But) it is important for us to remember why we do it and the people still living in these (flood prone) conditions – not just in the Valley but across Australia and the world.

“This type of work will occur more often to improve disaster resilience. And it is achievable within the current framework in which we work.

“Small steps on one project lead to bigger ones across the industry and ultimately, toward a future where we have a greater chance to mitigate the impacts of climate change and improve the resilience and safety of our communities.”

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